Hi, I would like to include additional comments. The end voltage, and even the voltage profile, are determined by a combination of electronic and ionic properties of the active material. Electronic properties are modified upon intercalation/deintercalation, where electron density variations at the valence/conduction bands will modify the Fermi level energy. The material voltage profile is highly dependent of this parameter. The ionic contribution to the voltage profile is related to the ion concentration in a similar way as on the Nernst equation. For more information:

H. Gerischer, F. Decker and B. Scrosati, The electronic and the ionic contribution to the free energy of alkali metals in intercalation compounds, J. Electrochem. Soc., Vol. 141, No. 9, 1994.       

1. de and intercalation of the anode material-

2. stability  in the solvent -

3. Exchange CD of the Electrochemical reaction

[A]The basic process that occurs in a rechargeable lithium ion batteries( LIB )is the intercalation of lithium ions into different host materials whose electrochemical properties ( specific capacity, reversibility, rate capability, cycling behavior) are strongly dependent on the structural changes induced by the lithium insertion reaction.

[B]When the cut off voltage reaches[ ideal =value 4.2V;but starts from 3.85V], the battery is expected to stop as there is going to be no more availability of electrons because the following half cell reaction is about to stop.

Li(s)------ Li(+)+e---------[1]

[C] At this point , the different materials like TiO2, V2O5, MnO2 come to its rescue as follows. I take the best compound among your self have cited .

(i) Taking the case of MnO2 present as LiMn2O4 . The products formed in[I] get added in it to give:

Li+ + LiMn2O4+e------ Li2Mn2O4

[D] Here the oxidation state( charge) of manganese is is +3[ It is Mn^3]

This loses an an electron as:

Mn^3----------Mn^4+e

So the electrons become available again and battery would continue to work.

[E] As regards the presence of different voltages:

[i] Si would not lose electon and the moment half cell reaction [I] stops, the battery becomes dead.

[ii] As regards to the remaining three, the Ti/ V/ Mn ions have different half cell potentials[ values are reported in literature], and thus the cells formed between Li and each one of these ions are expected to have different cell voltage[ because Li/Li(+) has a constant value of 3.05V].

Good

one can calculate the actual number of electrons transferred from Warburg impedance   of the cell

That is called as polarization effect.  If you exceed certain voltage that may affect the electrode material.

Hi, I would like to include additional comments. The end voltage, and even the voltage profile, are determined by a combination of electronic and ionic properties of the active material. Electronic properties are modified upon intercalation/deintercalation, where electron density variations at the valence/conduction bands will modify the Fermi level energy. The material voltage profile is highly dependent of this parameter. The ionic contribution to the voltage profile is related to the ion concentration in a similar way as on the Nernst equation. For more information:

H. Gerischer, F. Decker and B. Scrosati, The electronic and the ionic contribution to the free energy of alkali metals in intercalation compounds, J. Electrochem. Soc., Vol. 141, No. 9, 1994.       

Hi,

Voltage generation mainly depends on Fermi level of semiconductor 

Hello

the cell voltage is not important in a battery - it is the current - here exchange CD

I think the voltage matters a lot, especially during the discharge process. I claim this because that the battery discharge capacity is eventually determined by the Gibbs free energy of the whole electrochemical system. Therefore, if we consider one Li ion transfering from anode to cathode, the current density per each Li ion is determined by the voltage. As the battery discharge window is somehow governed by Fermi level alignment, the number transfer between the electrodes in a stable battery should be constant in a specific system. Actually, I prefer the idea from Dr. Montoro that the end state of the battery is generally marked by the intergrity of Galvanic potentials of the electrodes. Therefore, in a half battery, for example, the discharge window (marks with the starting voltage and end voltage) is mainly determined by the Fermi level of testing electrode and the work function of the Li. Pleasee correct me if I mistaked anything. Many thanks.

hello

In a lithium cell voltage is good even when it has reached cut-off

You may have the voltage but current will be low

due to internal resistance, electrode passivation and  lithium occupying unwanted sites, the electrode will give potential, but not current

ultimately we want current - we want lithium to travel but lithium should be available - locked in unwanted sites -now current will not flow

( i worked on primary secondary and lithium batteries - for nearly 15 years in batteries)

Thank you, Prof. Muralidharan. I start to understand your point now. Obviously, the current is blocked even the voltage remains due to the material issues. Just like you said, it might be caused due to poor conductivity of electrodes, electrode passivation (I am not sure what exactly it is, but is sounds electrode is somewhat failed to perform its function), and lithium occupying unwanted sites. I would like to ask two more questions:

1) lithium ion performs as positive charge carrier that transfer between the electrodes to keep the whole system electricla neutral. Is there any possibility that Li ions inside the electrode act as hooping sites that pass holes to the Li at the surface of the electrode?

2) I see in many works that there always more lithium ions intercalated into the electrodes than how much could deintercalated during the first cycle, usually up to 30-50% of total. Are all of these lithium ions locked at the wrong sites? If so are we looking forward to release all of them or we left part of them to maintain the structural stability in further cycles?

This is somehow important because it is a key to understand the importance of the discharge window of the battery.

reg first question of semi conducting  property i shall think ,

reg the second  ,  it always happen in all battery electrodes - the electrolyte should flow-- should be retained - in this case Li has to settle in the comfortable position- it  may take time  to replace of the substituent transition metal

loss in cycle life is due to lithium  being locked

Hi,

1. your first question isnt clear for me. 

2. Usually the Li battery materials (e.g. LiCoO2) are not submitted to a deep discharge (complete Li extraction). This situation can induce a serious coulombic efficiency loss with a fast capacity fading. These effects are often attributed to irreversible structural modifications ... in both structure or electronic states. You are right !! we left part of Li to maintain the structural stability. e.g. the LiCoO2 operates efficiently until Li0.5CoO2. A half of lithium is left in the structure to attain a high reversibility. LiCoO2 have a theoretical capacity of 274 mA.h/g, but a reversible (practical) capacity by 140 mA.h/g. Different materials have different reversible Li ranges ... The new Li(CoNiMn)O2 or the Li-excess layerd materials can operate with capacities as high as 250 mA.h/g ... with a large Li reversible range.   

i worked on Li cells

Li CoO2, Li NiO2 and Li MnO2 are good

substitutions with transition metals are also good

But the problem is during charge/ discharge Li should not go into non available sites

Reg the first question

has the semiconducting property any thing to with the exchange c.d ?

Many thanks, but I think we have gone a bit far from the question. My question is that what property of the material determines its working charge/discharge voltage?

ok

Dear @Liu, I do find this article Silicon nanofibres could boost lithium-ion battery performance appropriate for your thread.

"RESEARCHERS at the University of California have developed a novel paper-like material that could boost lithium-ion batteries.

The material is composed of sponge-like silicon nanofibres more than 100 times thinner than human hair, and could be used to boost by several times the amount of energy that can be delivered per unit weight of the battery.

The research has been published in a paper titled “Towards Scalable Binderless Electrodes: Carbon Coated Silicon Nanofiber Paper via Mg Reduction of Electrospun SiO2 Nanofibers,” in the journal Nature Scientific Reports..."

http://www.electronicsnews.com.au/news/silicon-nanofibres-could-boost-lithium-ion-battery